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Old 07-14-2006, 04:33 PM - Thread Starter
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I'm in the earliest stages of HT construction, and I'm working in an inherited semi-finished basement space. The previous owner (who should not be allowed to own tools more dangerous than a bottle opener,) finished about half this basement. My project will involve tearing out and moving back one of the existing walls to make the room larger so I can also put in a bar (and pool table!)

I see this as a media room. I have a 50" plasma to handle the video end, but I want to really be able to LISTEN to music as well. I am planning on acoustic treaments.

The drywall which currently covers the concrete walls on one side and the back of this space has no insulation at all behind it. Lazy B*stard that I am, I was thinking about using blown-in insulation to remedy this. The only other alternatives are either no insulation at all, or tearing down the existing walls and putting in the pink stuff, followed by re-drywalling all of it.

We live in a very dry climate at the top of a hill, so the odds of water in the basement are slim, ...although my next door neighbor did manage to flood his basement when he forgot to turn off his sprinkler and left for the weekend.

So the question: Is putting blown-in insulation between drywall and poured concrete below grade without a vapor barrier a really bad idea I should get out of my mind? I've talked to a couple of people over at Big Orange and no one really tried to talk me out of it, but I remain unconvinced.

Thanks!
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Old 07-14-2006, 09:45 PM
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As a general rule (from somebody who owns a second business called MoldBuster), it is a bad idea to put drywall and insulation over a concrete wall that has either no vapor barrier or sealer. You might try a vapor test if you have access to part of the concrete wall near the base... simply tape a 1' x 1' piece of clear plastic to the wall and let it sit for 24 hours. If you get condensation there...don't do it.

If you don't...you are still running a risk. Since you are in a dry climate, there is a good chance you don't have the waterproofing and water handling methods used in a wet climate (like ours here in the Pacific Northwest) so if you do get a period of heavy rain or you decide to put in plants along that side of the house (meaning watering), you may get a lot of water vapor intrusion. I'm currently remediating an entire complex of homes with moldy daylight basements from a builder who brought crews in from Arizona. They built good houses...for Arizona. In Washingon state, they are a disaster with big time mold after 3 months of occupancy.

Since a lot of blown-in is made from cellulose, it can retain a ton of water for a long time. Even if the blown in is treated, good chance your drywall will get moldy because the insulation can retain a large water load in the wall. There is NOTHING worse than having to tear apart a beautifully built theater because your GOM is turning fuzzy.

What you might think about instead if you don't want to tear out the drywall, is expanding foam insulation (ala icynene). I believe there may be forms you can inject. It has kick butt insulation properties and won't retain any moisture. The disadvantage is that it isn't cheap, so you may have to weigh the cost versus tearing out and replacing the rock.

"Did you make 'em fine-ass-soundin' speakers over there what would sound gooder than hell comin' out of the back of my truck-boat-truck?"

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Old 07-15-2006, 08:22 AM
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I think you should word that much more strongly. Uninsulated basement walls with no vapor barrier may have mold problems. Insulated ones with no vapor barrier *will* have mold problems. The insulation will exaggerate the moisture issues. Dont do it.

The closed-cell spray form (for example, 3M walltite) comes in a liquid form where they drill holes and pour it in. 1.5" of this is an effective vapor barrier.

Andy K.
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Old 07-15-2006, 02:29 PM - Thread Starter
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Thanks for the input, this room was originally finished probably at least 15 years ago and I've actually RotoZipped a couple of holes near the bottom in a couple of spots just to check and see if there was anything going on, and there wasn't. Still...I agree that the posibillty is there.

So if I decide to tear out the drywall, is a layer of visclean or plastic next to the concrete, with some fiberglass insulation between the studs a sufficient way to do this? Would I want to use the paper faced insulation? Which way would the paper face, to the room side?

Or should I just let the drywall stay with the air circulating behind it the way it is? They mounted the studs at least 1" in front of the concrete to allow for uneveness in the wall, so there is probably 4 1/2" of space behind the drywall currently.

Thanks again to everyone in this forum, and others, where so many generously share their knowledge!
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Old 07-16-2006, 09:28 AM
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Patrick,

You might want to search for vapor barrior. There have been a few threads about it. All I can remember from those threads is that it seems to vary significantly from location to location where you should put vapor barrior. I seem to recall that it varied quite a bit in hot climates (where the inside is air conditioned & the outside is hot), and colder climates where the inside is heated & the outside is cold. It seems there were variations on whether you can or must use kraft faced insulation. I think I recall someone else here in Colorado said they had to use kraft faced insulation in their area.

So, my plan when I get to that stage, is to call my local building inspector to find out what needs to be done here, and I'd recommend the same. It sounds like it could be a disaster if done wrong.

Guy
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Old 07-17-2006, 01:54 PM
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I agree with Guy. In fact, I would say for proper building techniques, if you want to use the internet as a resource (which is a fine idea) look for DIY-type websites and not necessarily this one. Use this one as a resource for HT-specifically related issues.

For example, to answer your questions, yes you could do a layer of plastic against the concrete, but it must only go from grade level to the floor, and be tucked under the stud wall. Then you need a full continuous vapor barrier on the inside of the room. This is the older method of insulating and it has been shown to be more prone to mold issues than using rigid foam. As for faced insulation the facing goes to the warm side which will be the inside in CO. But I am not that familiar with what else is involved in properly using faced insulation.

Andy K.
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Old 07-17-2006, 04:55 PM
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If you do a search here, there are even some threads on this very topic. Being in CO, you're in a similar boat as mine in Iowa. I did quite a bit of research before I started finishing my basement, and in the end I liked what I found at Building Science Corporation. Last I knew the PDF that I used that had a ton of excellent info in it is gone from their site, but I think it can still be found on the net. If you can't find, I can probably scrounge it up.

Basically, what they found through lots of site surveys (empirical data) was that in colder climates the old 'interior vapor barrior/insulation/concrete' concept doesn't work as well in practice as it would seem in theory. There's way too much to go into here, but essentially, the problem goes like this:

During the heating season, you have very cold concrete - sometimes extremely cold. You have lots of penetrations in the vapor barrier (outlets, switches, etc.) where warm humid air inevitably enters the wall cavity. That warm vapor travels away from the conditioned space toward the cold foundation (thermodynamics says so) where it condenses. Now you have condensation in an insulated space. You need heat and air to vaporize the condensation - which won't ever happen efficiently because the cavity is insulated! Then, the problem is compounded if you have water intrusion - it can get in, but it can't get out.

What Building Science Corp recommended (from memory) was no interior vapor barrier, unfaced insulation, and an XPS (closed-cell) board (which is a vapor retarder) against the foundation. The lack of vapor barrier allows the wall to dry to the interior, but the XPS raises the temperature inside the wall assembly enough (even in extreme cold) that condensation shouldn't occur. If it does, or if there is water intrusion from the exterior, the assembly can dry.

Of course, this is academic and so probably wouldn't pass code in many locales. The concept makes perfect sense to me, though and certainly wouldn't be the first time public policy wasn't the best way to accomplish something.

http://buildingscience.com/

Note - there are lots of schools of thought on this subject and as others have mentioned, it also depends on your climate and local building codes. Do your homework.

Sorry for the long post.

SC

I'm a Home Theater Enthusiast with GAS: Gadget Acquisition Syndrome.
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Old 07-19-2006, 01:22 PM - Thread Starter
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Thanks to you folks that responded. I appreciate your input. I just got off the phone with one of the local building inspectors, who told me that the answer is an unequivocal "it depends."

THe BI also recommended buildingscience.com as an excellent resource.

I think that for me the solution is going to involve sealing all possible airleaks, then using unfaced fiberglass insulation between the studs, leaving some airspace between the back of that and the concrete foundation.
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Old 07-21-2006, 09:30 PM
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patrickjherbert,

The key to the Building Science recommendations is that you must accept the fact that moisture-laden vapor will get behind your wall and you must provide a way for it to dry out.

Thus, they recommend up to 2" of EPS or 1" of XPS (with no plastic facing on it) against the concrete wall. Both will breath (though the EPS more so), and will allow drying, which a simple plastic vapor barrier will not. So although they are foams that appear "solid", they actually are slightly porous.

Also, kraft paper-faced insulation is fine. The paper will also allow vapor transmission. Just stay away from any foil-faced stuff.
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Old 07-21-2006, 11:12 PM
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The absolute easiest way to get around the vapor barrier problem is to properly seal the wall itself and forget the plastic. Assuming they didn't paint the wall, sealing the concrete solves the problems (we do it all the time here in wetstern WASHington with phenominal before and after results). If you have block, you'll need a different sealer product than a poured 'crete. The only thing I don't think you can do it on is AAC...but you are unlikely to have that. Best thing about sealing the 'crete is that critters can't get thru it and you don't have the issues with vapor build up running down the wall and exiting the base (the water has to have somewhere to go). You also do want to leave that space so there isn't as much of a temp differential...though that isn't as big a problem with below grade walls unless you live above the permafrost line or you like to keep your house HOT.

There are other steps you can take such as using a construction grade mold preventative coating on the baseboard and timbers, and using a paperless drywall and non paper backed insulation.

"Did you make 'em fine-ass-soundin' speakers over there what would sound gooder than hell comin' out of the back of my truck-boat-truck?"

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Old 07-22-2006, 08:05 AM
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Actually, that is completely wrong. Sealing the concrete from the outside does a very good job of waterproofing moisture coming in from the outside. Sealing the concrete from the inside does a mediocre-to-poor job of it.

Neither will solve the problem of moisture from the *interior air* passing through the insulation and condensing on the cold side of the wall....

Andy K.
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Old 07-22-2006, 09:16 PM
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Even if you seal the outside of the wall, moisture will still wick up from the footings. That's why Building Science recommends a plastic barrier on top of the footing to decouple it from the wall (so the plastic goes under your floor and between the concrete walls and their footing).

I don't know how much moisture would actually wick up (I would think it would be just a small fraction of what would come through the outside face of the walls), but Building Science has that in their recommendations none-the-less.

Scott
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